This board would be a great way to add an 80-column terminal but the chip is essentially unobtainable.

An alternative chip would be the EF9345 chip, which is still available. This can produce 80 or 40 column text, and has colour capabilities. It was used in an 80-column board designed by the Dutch Acorn Atom user group, to allow CP/M programs to run. Therefore there should be some ready-made firmware for it. The master clock is 12 MHz, and the dot rate is 8 or 16 MHz, just like the BBC micros, so the pixels are not exactly square.

The EF9345 has no graphic modes - for that you would need the EF9366. There is a documented design by Rolf-Dieter Klein, written in German. It has example software in Z80 assembler and the BASIC his Z80-board, but the document scan quality is very poor and OCR fails to extract anything you could use to start recreating a source file - you'd have to read it and type it in.